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Home , Quaternary glaciation

Discovering the

Jarðsaga 2 Ólafur Ingólfsson Háskóla Íslands Defining the

The Quaternary Period is a subdivision of geolo- gical time which covers the last 1.8 MY, up to the present day. The Quaternary can be subdivided into two epochs; the (1.8 MY-10 ka) and the (10ka-present)

The Quaternary Period has been one of extraordinary changes in global environ- ments as well as the period during which much of the of Man took place. The Pleistocene The term Pleistocene ("most recent") was coined by Lyell in 1839, on the basis of a section of type strata in eastern Sicily, according to the proportion of extinct to living species of mollusk shells in the sediment. Strata with 90 to 100% present day species were designated Pleisto- cene. Clearly this is a somewhat arbitrary arrangement, and in any cases many strata do not contain mollusk shells.

• The present definition of the Pleistocene is based on radiometric dating of 1.8 MY or more recent, the presence of cooler water mollusks and foraminifers, and on land the remains of modern horses and true (in the past more widespread than they are today). A Pleistocene journey towards ever harscher environments

Conspicuous trends through the Quaternary: • Ice volumes increase and global sea levels fall •The amplitude of change during -glacial cycles increases. Duration of Glacial Cycles increases. • are very brief periods in an overall cool- cold • 2,6-0,8 MY ago: Glacial cycles ~ 40,000 . Periods of glacials and interglacials of similar duration • After 0,8 MY ago: Glacial cycles ~ 100,000 years. Glaciation periods increase in duration, interglacial periods remain brief periods in an overall cool-cold climate. TheIceAgeconcept

Since the middle of the l9th century geologists realised that during the most recent period of geological time ("The Ice-Age") there had been large changes in the landscape and the environment.

It was widely accepted that the action of had pro- foundly altered the surface of the over wide areas, including most of northern and . Glacial erratics – a key to the Ice Age theory

Erratics are one very obvious signature of former glaciations: Scandinavian rocks on NW European sediments; Canadian rocks on the great plains of USA; Alpine rocks on European lowlands, etc

The track of a is as unmistakable as that of a man or bear. John Strong Newberry (1870). Theories cooked up to explain erratics

Few early naturalists had experience with modern glaciers. Early theories to explain large erratic blocks include: • 1815 - “Rollstein” or mudflow theory (von Buch, von Humboldt, Sefström) • 1823 - Diluvium theory (Buckland) • 1833 - Drift theory (Lyell, Darwin) Discovery of the Ice Age • 1787 - Kuhn, a Swiss minister, attributes erratic boulders near Grindelwald to glacier contraction. • 1795 - Hutton, English geologist, publishes Theory of the Earth, where he describes how ice transported granite erratics to the Jura Mountains. • 1795 – Sveinn Pálsson’s “Book on Glaciers” recognizes more extensive glaciations in the past (not published until 1945). • 1815 - Perraudin, a Swiss mountaineer and hunter, argues that glaciers had at one time extended well into the Val de Bagnes in the . • 1823 - Goethe, a German poet, takes note of findings by scientists of erratics on the North German Plains and publishes the novel Wilhelm Meister in which he promotes the idea of “Eiszeit” or ice age. • 1824 - Esmark, a Norwegian naturalist, argues that the glaciers of Norway had once been more extensive. • 1829 - Venetz, a Swiss engineer, argues that glaciers once covered the Jura and Swiss plain. • 1837 - Agassiz, a Swiss zoologist and president of the Swiss Society of Natural Sciences, presents a lecture explaining the origin of erratics by glacier transport. Louis Agassiz (1807-1873) • Observing the glaciers of his native Switzerland, Agassiz noticed the marks that glaciers left on the Earth: great valleys; large boulders; scratches and smoothing of rocks; pushed up by glacial advances.

• He realized that in many places signs of glaciation could be seen where no glaciers existed. Previous scientists had explained these features as made by icebergs or floods; Agassiz integrated all these facts to formulate his theory that a great Ice Age had once gripped the Earth, and published his theory in Étude sur les glaciers (1840). Later book, Système glaciare (1847), presented further evidence for his theory, gathered all over Europe. • Like many of the 19th century naturalists, Agassiz was educated in the medical tradition and qualified as a physician. Received the Ph.D. in the spring of 1829 from the Univ. of Erlangen. • In 1832 he accepted a position as professor of natural history at the Lyceum of Neuchâtel in Switzerland, where he developed his ideas on continental glaciation and earth history. • In January 1848, Agassiz took a professorship in zoology and geology at Harvard College. Agassiz always regarded himself as a zoologist, rather than physicist or geologist. Founded the Museum of Comparative Zoology at Harvard University. http://www.mcz.harvard.edu/Departments/Fish/

“I have devoted my whole to the study of , and yet a single sentence may express all that I have done. I have shown that there is a correspondence between the succession of Fishes in geological times and the different stages of their growth in the egg...” (1869). Interestingly enough, Agassiz was a creationist and opposed Darwins ideas...! European scientists debated the Glacial Theory for 25 years! • The Swedish pioneer of polar research, Otto Torell (1828-1900) visited Iceland and in the mid-19th Century to study glaciers and glacial deposits. • In 1875 he convinced the Germans that bits and pieces of Scandinavia had been scattered over continental NW Europe by the Scandinacian Inland Ice. A church built of Scandinavian granites – brought in by the ice

The 12th Century church St 3) Siljan-Granit; 4)Växjö-Granit; 5 & Marcus, in Marx, southwest 11) Småland-Granit; 12) Åland-Granit of Vilhelmshafen, Friesland, is built of assorted granite blocks. These were brought to the area by glaciers advancing across the . http://www.nihk.de/index.php?id=134 The glacial fingerprinting A. Morphological data:

1. Landscapes shaped by glacial action 2. Glacial striae on and boulders, glacial drift on surface 3. Terminal moraines and sandur areas 4. Isostatic fingerprinting: Distribution and altitude of raised beaches The glacial fingerprinting...

B. Stratigraphical data:

1. Lithostratigraphical data: tills, glaciofluvium, glaciomarine sediments. 2. Biostratigraphical data: fossil shells, pollen, macrofossils 3. Seismostratigraphical data from the shelf areas Glacial erratics Glacial drift and striated surfaces Glacial landscapes Valleys and fjords shaped by glacial action U-shaped valleys

Horns and arrêtes Raised beaches and

Evidence of Isostatic Rebound: In areas formerly covered by ice sheets (around the Baltic Sea and , for example), sea cliffs and beach ridges are now found nearly 300 m above ! 14C ages on marine shells and driftwood show that these features are postglacial (less than 14,000 years old). They were formed at sea level and, even though eustatic sea level has risen, they have risen far more from isostasy. Ongoing Glacioisostatic Recovery: An example of rebound can be found in Scandi- navia. The northern Baltic Sea is rising nearly 1 cm/ , or 1 m century. Isostatic recovery on Iceland very fast... A huge glaciation in the not too distant past...

Enormous discussion as to the nature of an Ice Age Monoglacialists vs multiglacialists Once widespread acceptance of the concept of ice ages was in place, the stage was set for a remarkable discovery: the Earth has been subject to numerous ice ages over the course of its existence. Geikie theorized five interglacial periods had occurred in Britain. Penck and Bruckner, in 1909, noted remnants of four sets of river terraces in the outwash gravels in the northern foothill valleys of the Alps. Monoglacialists accepted that there had been an Ice Age, but did not accept that the Ice Age had consisted of a number of glaciations, seperated by ice free interglacials. A very bitter dispute in Iceland

Helgi Pjetursson (1872-1949) was a pioneer in developing the theory of Ice Ages. In his doktoral thesis from 1905 he proposed that Iceland had been subjected to more than one major glaciation.

The leading Icelandic naturalist at the time, Thorvaldur Thoroddsen (1855-1921), was a staunch monoglacialist and he basically went out of his way to destroy Helgi Pétursson’s reputation. Despite being the first Icelandic scientist ever to write a doctoral thesis in geology, Helgi Pjetursson never got a job doing research in Iceland. Fingerprinting of older Ice Ages discovered... Following establishment of an ice age in Europe and N America, geologists looked for evidence of ice ages in older rocks.

1856 - glacial sediments described from 1859 - Permian glacial sediments located in 1868 - Permian glacial sediments (Dwykka tillite) found in 1891 - glacial sediments described from Scotland and Norway Stratigraphy suggested more than one glaciation Distinct zonation in terminal moraines suggested repeated glaciations. This was confirmed by till stratigraphical studies. Glacial stratigraphy: repeated glaciations Classical division of the Quaternary

From: Lowe & Walker 1998: Reconstructing Quaternary Environments. Harlow, Longman. Once glaciations were accepted, their cause was up for discussion

In the 1870s the Scottish scientist was first to come up with a comprehensive theory explaining glacial cycles. His theory was based on the amount and distribut- ion of energy received by Earth from the sun. Crolls theory... • While the total amount of insolation received at a given latitude did not vary from year to year, the amount received in a given for a given latitude could vary significantly from year to year because of changes in the earth's orbit. • These seasonal variations were caused by two orbital phenomena known as precession (“möndulvelta”) and eccentricity (“hjámiðja”) . • While the initial climatic effect of changes in the earth's orbit might be rather small, but that these changes were amplified significantly by climatic feedback mechanisms in the earth's . http://www.ngdc.noaa.gov/paleo/slides/slideset/11/index.html Orbital changes Today’s situation Viewed in the present, the tilted earth revolves around the sun on an elliptical path. The orientation of the axis remains fixed in space, producing changes in the distri- bution of solar radiation over the course of the year.

These changes in the pattern of radiation reaching earth's surface cause the succession of the . The warm weather of summer comes to the , for instance, because during these months the northern hemisphere is tilted towards the sun (at the same time, the southern hemisphere experiences winter because it is tilted away from the sun). Precession (“möndulvelta”) Precession

It takes 19.000- 23.000 years to complete one precession cycle

Like a spinning top, the earth's orbit wobbles so that over the course of a precessional cycle, the traces a circle in space. The position of the equinoxes (“jafndægur”) and solstices (“sólhvörf”) shifts slowly around the earth's elliptical orbit. Precession changes the date at which the earth reaches its perihelion (“sólnánd”) serving to amplify or dampen seasonal climatic variability. Effects of Precession through time

The earth currently reaches its perihelion on January 3, close to the Northern Hemisphere's winter solstice. This timing of the perihelion and Northern Hemisphere's winter solstice reduces seasonal differences in insolation in the Northern Hemisphere because the hemisphere is closer to the sun in winter and hence relatively warmer. On the other hand, the earth is further away from the sun and relatively cooler during the Northern Hemisphere's summer, reaching its aphelion on July 5. However, 11,000 years ago, the reverse was true: the earth reached its perihelion during the northern summer, increasing the seasonal variability of earth's climate. Eccentricity The shape of the earth's orbit “hjámiðja” varies from nearly circular. These variations occur at a frequencies of 100,000 years and 400,000 years. Variations in have a small impact on the total amount of radiation received at the top of earth's atmosphere (on the order of 0.1%), but the eccentricity cycle modulates the amplitude of the precession cycle. During periods of high eccentricity (a more elliptical orbit), the effect of precession on the seasonal cycle is strong. Milankovitch Croll's arguments provoked a great deal of debate and research. In the 1910’s Milutin Milankovitch began a series of calculations that would eventually revive the orbital theory of . Milankovitch's main contributions were threefold:

1) He used new astronomical calculations that took into account a 3rd cyclical variation in the earth's orbit: tilt (obliquity – “möndulhalli”). 2) He reasoned that summer rather than winter tempera- tures were the main contributors of oscillations. 3) He calculated summer radiation curves for the key latitudes of 55, 60, and 65 degrees N that correlated well with evidence then available from the geologic record. (“möndulhalli”) Effects of changes in the axial tilt

Earth's axial tilt varies from 24.5° to 22.1° over the course of a 41,000-year cycle. Changes in axial tilt affect the distribution of solar radiation received at the earth's surface. When the angle of tilt is low, polar regions receive less insolation. When the tilt is greater, the polar regions receive more insolation during the course of a year. Like precession (“möndulvelta”) and eccentricity (“hjámiðja”), changes in tilt thus influence the relative strength of the seasons, but the effects of the tilt cycle are particularly pronounced in the high latitudes where the great ice ages began. The combined effect...

http://www.rt.is/ahb/sol/mbl.html Insolation curve for 65°N Marine evidence for numerous glaciations

Marine geological studies on sediment cores provide a much more continuous record of glaciation than terrestrial deposits do. The reason for this being that subsequent waves of glaciation often erased or altered traces of earlier glacial and interglacial periods. Evidence from sediment cores Sediment cores from the ocean floor contain information on fluctuations of global climate. Important infor- mation comes from the microscopic shells of forams:

• Different species of forams prefer different ocean temperature and nutrient conditions. Much about the climatic conditions of a core site in the past can be learned by by looking at which species once inhabited the area. •The shells of forams lock in the oxygen and carbon isotop- ic composition of the waters in which they formed. Because past periods of glaciation changed the relative quantities of 18O and 16O, the isotopic composition of foram shells as a proxy signal for past changes in global ice volume. Climate forcing on glacial-interglacial timescales

This figure summarizes our current understanding of the climate forcing, and the climate response that we observe in the geologic record on glacial – interglacial timescales. The top panel is June insolation at 65°N, in watts/m2.The three lower panels are all geologic records of glacial-interglacial change. δ18O in foraminifer skeletons is affected by both temperature and the amount of 16O locked away in ice sheets. Insolation and global ice volume fluctuations

When the data are filtered for solar insolation and global ice volume over the past400,000 years, weseethatinsolationandglobalicevolumefluctuatedat the same major frequencies: the precession (“möndulvelta”) cycle of 23,000 years and 19,000 years, the tilt (“möndulhalli”) cycle of 41,000 years, and the eccentricity (“hjámiðja”) cycle of 100,000 years How many - Quaternary glaciation cycles?

Pherhaps >30! Changing The relative importance of the three orbital cycles – eccentric- orbital ity (“hjámiðja”), obliquity (“möndulhalli”), and precession dominance (“möndulvelta”) - has not been constant in the past. The 18O curves from a pelagic sediment core spanning the last 2.6 MY show that the 41 ka obliquity cycle dominates the early part, with the result that glacials and interglacial were of roughly equal length. For the last 800 ka, the 100 ka eccentricity cycle has dominated, with glacials 5-10 times longer than interglacials. The reason for that is not clear. The orbital factors too small to matter in a hothouse world... The amount of heat received at higher lati- tudesisless thanthatat lowerlatitudes for three reasons. 1) a ray of solar radiation that strikes Earth at a high latitude is spread over more area than an equal ray that is perpendicular to Earth's surface at a lower latitude, 2) the high-latitude ray also passes through a greater thickness of atmoshpere, and 3) more of the ray's energy is reflected due to the low angle at which it strikes Earth's surface.

...but of crucial importance in an ice-house world where global tectonics restrict global distribution of energy Brief summary

• Ideas on a past Ice Age started developing in the late 18th Century. • Agassiz theory of Ice Ages (1840) was based on empirical data, but did not become generally accepted until the 1870’s. • It was soon realized that Earth had been subjected to a number of major glaciations, and that the last Ice Age had consisted of a number of glacial and interglacial periods. • Croll and later Milankovitch described the orbital parameters that cause periodic fluctuations in nergu from the sun. • Geological data (deep sea sediment core data, data etc) strongly support the periodicity suggested by the Milankovitch theory. • Feedback effects in Earth’s complex atmospheric and oceanic systems modify insolation changes. References used for this lecture

Stanley: Earth System History. Arnold, London http://www.ormstunga.is/islenska/itarefni/jon_eyth_um_thoroddsen.htm Lowe & Walker 1998: Reconstructing Quaternary Environments. Harlow, Longman. http://www.emporia.edu/earthsci/student/sedlacek1/website.htm http://www.palaeos.com/Cenozoic/Quaternary.htm http://www.ucmp.berkeley.edu/index.html http://www.ngdc.noaa.gov/paleo/slides/slideset/11/index.html http://www.rt.is/ahb/sol/mbl.html http://www.geo.oregonstate.edu/people/faculty/clark_publications/clarketal.- science1999.pdf http://www.mcz.harvard.edu/Departments/Fish/ http://www.oulu.fi/~spaceweb/textbook/crays.html http://pubs.giss.nasa.gov/docs/2001/2001_ShindellSchmidtM1.pdf http://www.ucmp.berkeley.edu/history/agassiz.html http://www.owlnet.rice.edu/~echollet/introduc.html